Being new to the list (having just bought my first MG - a '74 MGB w/
chrome bumpers) maybe it's fitting I reply to someone who seems new to
electrical problems.
The red dash light indicates a low rate of charge (a.k.a. 'current'
measured in 'amperes') is going back to the battery. This is either
because the alternator is delivering a low current or because something
else is using the current so there is little left to recharge the
battery.
The reason your light dims when you rev the motor is because you're
spinning the alternator (or generator) faster, thus creating more
current.
It would be worse at night because you have the headlamps on. Second
only
to your horn, these use more current than anything else in the car.
You say you have a carburettor with an electric choke, and that this
symptom appears in cold weather and ceases when the motor warms up. I
think in your case, I'd inspect the wiring to the choke. Is there a
short, (say from worn piece of insulation) somewhere in the circuit? Is
there a short in the circuitry within the choke mechanism? That it
backfires is interesting - could it be that due to a short, the choke is
kicking in and out and changing the mixture as you drive?
Remember that in general, cold temperature has a bad effect on battery
performance. Foul weather also seems to compound problems with
corrosion
on battery terminals and other electrical connections. (I wasn't much
of a
chemistry student so I can't give you the technical explanation, but
having
worked in a service station in winter, I've seen enough evidence.)
Also, if your
battery cables or alternator wiring are getting old, they may be
starting
to corrode or deteriorate internally, impeding current flow. If your
charging system is a poor performer much may be gained by replacing the
battery cables, ground straps and alternator wiring. (Particularly long
cables,
such as found on a battery not in the engine compartment are more
susceptible
to internal resistance.)
Of course, you always perform proper maintenance, so I need not suggest
you clean your battery terminals, top up your water level and check the
tension on your alternator belt, right?
Regards.
- Matt Kulka
(Flames regarding the length of this post will be cheerfully accepted.
I'm new here and just getting the hang of things.)
>>> ckr <ragthyme@fls.infi.net> 03/17/97 10:47am >>>
Friends:
I've got a little puzzler for you all. Here are the facts:
When my MGB starts in cold weather, the red dash indicator (alternator)
comes on, and stays on (nearly as I can tell) until the choke cuts out.
It waxes and wanes in intensity, depending (absurdly enough) on how hard
I'm punching the throttle ... more punch, less glow; less punch, more
glow. (!!!) It's also worse at night, when I have the lights on, though
it does happen during the day. This only happens when the temp is
below about 35F, and, oddly enough, totally goes away when the car has
warmed up. It doesn't otherwise seem to affect performance (though the
car backfires like bloody hell when it's cold).
Here's the car (for those of you not familiar with it):
75 MGB, 79 motor. Headers, free-flow exhaust, Weber downdraught 32/36
carb with electric choke. Slightly upgraded headlamps (sealed haologen)
and no emissions controls left (except the carbon cannister). On the
79 motor, I've got a 74 water pump and plastic fan, the original 75
radiator. 72 25D distributor, vaccuum advance sealed off, fresh points
and tuneup, correct N9YC plugs. Don't blame me for this Frankenstein
setup ... except for the carb, this is how I got the car. :) Alternator
is a rebuilt Lucas unit, installed last year. Battery is a fresh Series
26 Interstate, new cables, in a battery box.
Any thoughts?
TIA
Corey
75 MGB 'Rags'
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